Handle utf-8 decoding error with backslashreplace option. am: e3f93faa90 am: 3737defe14 am: 0a1132147f

Original change: https://android-review.googlesource.com/c/platform/tools/test/openhst/+/1427008

Change-Id: Ic2e7380f5e8d04b599a277cdf318bbf4a319a69d